The present invention relates to the field of optical systems and more particularly to coherent optical packet detectors.
Recent improvements in the wavelength division multiplexing (WDM) optical networks have led to transmission data rate up to 100 Gb/s per channel.
Thus, a transparent network provides huge capacity to transmit data from an ingress to an egress node.
However, such performances require devices achieving coherent detection of such signals at the egress node. FIG. 1 represents a coherent receiver used in high modulation rate WDM optical networks. Said receiver comprises two combining units 1 allowing to combine an incoming signal 3 which is splitted by a polarization beam splitter 5 with the signal provided by a local oscillator 7. Said combining units 1 comprises λ/4 optical filters 9, half mirrors 11 and polarization beam splitters 5 that allow to obtain four signals that are sent to four different photodiodes 13. The signals coming from the photodiodes 13 are then converted by analog to digital converter (ADC) 15 and transmitted to the digital signal processing unit 17. At the output of the DSP unit 17, signals are transmitted to the bit error rate (BER) decoding unit 19. The details of the digital processing unit 17 are represented in FIG. 2. After conversion in the ADC 15, signals are transmitted to a sampling scope 21 and then to a re-sampling unit 23. After re-sampling, chromatic dispersion units 25 achieve a coarse filtering of the residual chromatic dispersion. A unit 26 may therefore refers to the coarse filtering of the chromatic dispersion. Digital clock recovery is then achieved in the unit 27, then the polarization demultiplexing and equalization unit 29 achieves a fine compensation for the residual chromatic dispersion. Signals are then transmitted to frequency and carrier phase recovery units 31, symbol identification units 33 and are then transmitted to bit error rate decoding units 19. Thus, such equipments allow to process optical signals having high modulation rates.
In order to improve the flexibility of the network, a possible next step is the aggregation of different signals along an optical channel in order to optimize the network capacity.
However, it turns out that the detection devices used in legacy circuit networks, as the one previously described in FIG. 1 and FIG. 2, are not adapted because they are too slow, in particular the step corresponding to the coarse filtering of the residual chromatic dispersion (unit 26) which is based on adaptive methods and which requires the convergence of the method and/or the selection of optimized filtering parameters. In the same way, the devices used for the filtering of the other linear physical impairments such as the polarization mode dispersion are too slow to achieve efficient filtering in the required time range.